1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) adaptive antenna receiving apparatus and more particularly, to a CDMA adaptive antenna receiving apparatus for separating and synthesizing a plural of desired signal components incoming at a plural of different timings and from a plural of different directions at each timing.
2. Description of the Related Art
The CDMA system capable of developing greatly a capacity for subscribers has been remarkable as a multiple access system for use in a mobile communication system including a base station and portable mobile stations.
The CDMA adaptive antenna receiving apparatus for use in a CDMA mobile communication system is subjected to eliminate the interference by means of the directivity of the antenna. This is explained in xe2x80x9cTDL Adaptive Array Antenna Employing Spread Process Gain for Spectrum Spread Multi-dimensional Connectionxe2x80x9d, Oho, Kohno and Imai, Electronics Information and Communication Society Journal, vol. J75-BII, No. 11, pp. 815-825, 1992. This is also explained in xe2x80x9cCharacteristic of Decision Feedback type Coherent Adaptive Diversity in DS-CDMAxe2x80x9d, Tanaka, Miki and Sawahashi, Electronics Information and Communication Society, Radio Communication System Study Group Technical Report, RCS96-102, November 1996.
FIG. 5 is a block diagram showing an example of the conventional CDMA adaptive antenna receiving apparatus, so-called RAKE receiver. Defining N (N is an integer of 2 or more) for the number of receiving antennas and M (M is an integer of 2 or more) for the number of multi-paths, a CDMA adaptive antenna receiving apparatus for No. k user (k is an integer of 1 or more) will be explained. Signals received at antennas 110-1 to 110-N are classified into a first through No. M paths in accordance with delay times thereof, and are introduced into delay circuits 120-2 to 120-M and adaptive receivers 130-1 to 130-M. Delay circuits 120-2 to 120-M may delay the input signals so as to synchronize with the first path. Delay circuit 120-1 having a time delay of 0 is omitted from the drawing. Outputs of the adaptive receivers are summed at adder 140 and the output therefrom is fed into decision device 150. The output signal from decision device 150 is not only output as a reception symbol of the No. k user but also sent to adaptive receivers 130-1 to 130-M.
Adaptive receivers 130-1 to 130-M have the same construction. FIG. 6 shows the adaptive receiver for No. m path (1xe2x89xa6mxe2x89xa6M). Received signals are despread by despread devices 161-1 to 161-N, and are thereafter sent to multipliers 1621-1 to 162-N and delay circuit 163. The received signals are multiplied by reception weights at multipliers 161-1 to 161-N and then are summed for weight synthesizing at adder 164. The reception weights are components of a vector. Each component of the vector is employed at multipliers 161-1 to 161-N. The weight-synthesized signal is sent to multiplier 165, communication channel estimating device 166 and subtracter 169. Communication channel estimating device 166 may estimate a communication distortion based on the output from 164. Complex conjugate generator 167 generates a complex conjugate number of the communication distortion that is multiplied by the output of adder 164 at multiplier 165. The output from multiplier 165 is a demodulated signal to be sent to adder 140 shown in FIG. 5. The outputs from adaptive receivers 130-1 to 130-M are added with each other at adder 140 for performing the RAKE synthesis, and then a data symbol is decided at decision device 150.
In adaptive receiver 130-m (1xe2x89xa6mxe2x89xa6M), the output from decision device 150 is multiplied by the communication channel distortion output from communication channel estimating device 166 to be input into subtracter 169. Subtracter 169 computes an error by subtracting the output of adder 164 from the output of multiplier 168. The error is fed to adaptive update device 170. Adaptive update device 170 updates the reception weight vector by using the error from subtracter 170 and the signals that are received at the antennas and delayed by a demodulation time at delay circuit 163. A known algorithm (for example, Least Mean Square Algorithm) may be available for the adaptive update algorithm.
The conventional technology has an disadvantage in which the plural desired signals incoming from different directions at the same time can not be separated and synthesized. This is because only one reception weight vector is provided per adaptive receiver.
Another disadvantage of the conventional technology is that the convergence speed of the reception weight vector is slow and the response is low. This is because the process for deciding the initial value of the reception weight vector is identical for any communication channel, and the previous reception weight vector before interruption is not employed at the beginning of next update operation.
An object of the present invention is to provide a CDMA adaptive antenna receiving apparatus capable of separating and synthesizing the plural desired signals incoming from different directions at the same time.
Another object of the present invention is to provide a CDMA adaptive antenna receiving apparatus having an advantageous convergence speed of a reception weight vector and response.
The CDMA adaptive antenna receiving apparatus according to the present invention comprises a plural of adaptive receiving units in each adaptive receiver. This constitution enables to provide a directivity for each of desired signals incoming at different timings and from different directions at the same time, and thus the first object may be achieved.
The present invention further comprises a means for controlling the reception weight vectors. This constitution enables to anticipate the incoming directions of the desired signals, and thus the second object may be achieved.